The present invention relates to voltage measuring systems and specifically to a high voltage measuring system having a high input impedance for use in measuring high voltage, low amplitude signals from high impedance sources.
Certain high voltage, low current power supplies generally have very high output impedances. Such power supplies might be used to drive an image converter or an intensifier tube, for example. Performing voltage measurements on such power supply outputs is difficult because of their high output impedances, principally because it is difficult not to load down such power supplies with conventional measuring equipment, which then introduces error into the measured readout. For example, to obtain less than 0.1% measurement error, the measuring device must have an input resistance that is at least 100 times greater than the output resistance of the high voltage power supply being tested. If the power supply already has high impedance, such as in the megohm or gigohm range, then the measurement equipment must have an input impedance in the terohm range. By way of example, a model ESH-1X electrostatic volt meter, manufactured by Sensitive Research, Inc., may be used to measure 7500 volt, 10 gigohm voltage sources.
There are many industrial measurement applications, however, which require remote monitoring capabilities for high voltage supplies, i.e., for sensing parameter signals at one location and transferring information representative of the sensed parameter signals to another location. By way of example, such remote monitoring capability may be important when the supply is in a hazardous environment. One approach suitable for performing such remote monitoring is disclosed in U.S. patent application No. 422,133, now U.S. Pat. No. 5,013,154 (KML-118), assigned to the assignee of the present invention. In accordance with that approach, a conventional electrometer may be connected to the source to be monitored in the hazardous environment. A remotely located video generates data representative of an image of the electrometer needle and scale, and that data is analyzed to identify the position of the needle relative to the scale. While this approach is effective to provide remote measurements of a high voltage, high impedance supply, there is a relatively high cost associated with such measurements due to the requirement for a video camera. Moreover, the image data is converted to output voltage data based on a conversion of the image data texts compared to a look-up table, rather than directly measured information.
It is an object of the present invention to provide a high input impedance voltage measuring system for remotely reading sensed voltages.
Another object is to provide an improved system for measuring voltages at a high impedance source.